The present invention relates to magnetic memory cells, and more specifically, to devices and methods for fabricating a parallel shunt path that reduces voltage biases in thermally assisted magnetic memory cells.
Switching of magnetic solid state memory devices (i.e., magnetoresistive random access memory (MRAM)) requires significant amounts of electrical current, either in the write lines (to produce magnetic fields) or through the device itself (using the current to switch via spin torque). In particular, as the device size is scaled down (for field MRAM) the current required to produce fields are too large to be sustained by the field-producing wires. For spin-torque devices, the required switching currents and voltages are large enough that device breakdown can occur too close to the switching threshold to ensure that all devices in the array switch without causing damage.
Heating the device can be advantageous in that the selected (heated) device changes properties in such a way as to reduce the switching field or current substantially. This reduction can arise due to a change in the properties of the magnetic films, or through a reduction in the exchange interaction between the pinning antiferromagnet and the magnetic films. Several schemes for heating a magnetic tunnel-junction (MTJ) device have been discussed. A common conventional method for heating MTJs is passing a current through the tunnel junction itself. However, in order to attain sufficient heating (typically of order hundreds of degree temperature rise), a constraint occurs in that the barrier breaks down before sufficient temperature rise is obtained.
Significant work has been done in order to reduce the required temperature for operation, to increase the temperature rise obtained by a given power and to increase the voltage breakdown limit in order to increase the available power. However, it is desirable to have higher temperatures achievable without endangering the integrity of the tunnel junction barrier, for example to have a wider range of operating temperatures.